Add a proper description to a tracing::trace() that clarifies
that the tracing message string and the positional parameters
are going to be copied if tracing state is initialized.
Add a description for trace_state::begin() methods and for a
tracing::begin() helper function.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Sometimes we want to be able to set "params" map after we
started a tracing session, e.g. when the parameters values,
like a consistency level parsed from the "options" part of a binary frame,
are available only after some heavy part of a flow we would like
to trace.
This patch includes the following changes:
- No longer pass a map to the begin().
- Limit the parameters to the known set.
- Define a method to set each such parameter and save its
value till the final sstring->sstring map is created.
- Construct the final sstring->sstring map in the destructor of the trace_state
object in order to defer all the formatting to be after the traced flow.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
- Extend the i_tracing_backend_helper interface to accept the event
record timestamp.
- Grab the current timestamp when the event record is taken.
- Add the instrumentation to the trace_keyspace_helper to create a unique time-UUID
from a given std::chrono::duration object.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
This helper returns an std::experimental::optional<trace_info>
which is initialized or not initialized depending on whether
a given trace_state_ptr is initialized or not.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Add an support for passing a format string plus positional parameters
for creation of a trace point message.
Format string should be given in a fmt library native format described
here: http://fmtlib.net/latest/syntax.html#syntax .
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Prevent the destruction of tracing::tracing instances while there
are still tracing::trace_state objects that are using it:
- Make tracing::tracing inherit from seastar::async_sharded_service<tracing::tracing>.
- Grab a tracing::tracing.shared_from_this() in each
tracing::trace_state object using it.
- Use a saved pointer to the local tracing::tracing instance in a destructor
instead of accessing it via tracing::get_local_tracing_instance()
to avoid "local is not initialized" assert when sessions are
being destroyed after the service was stopped.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
In names of functions and variables:
s/flush_/write_/
s/store_/write_/
In a i_tracing_backend_helper:
s/flush()/kick()/
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
trace_state: Is a single tracing session.
tracing: A sharded service that contains an i_trace_backend_helper instance
and is a "factory" of trace_state objects.
trace_state main interface functions are:
- begin(): Start time counting (should be used via tracing::begin() wrapper).
- trace(): Create a tracing event - it's coupled with a time passed since begin()
(should be used via tracing::trace() wrapper).
- ~trace_state(): Destructor will close the tracing session.
"tracing" service main interface function is:
- start(): Initialize a backend.
- stop(): Shut down a backend.
- create_session(): Creates a new tracing session.
(tracing::end_session(): Is called by a trace_state destructor).
When trace_state needs to store a tracing event it uses a backend helper from
a "tracing" service.
A "tracing" service limits a number of opened tracing session by a static number.
If this number is reached - next sessions will be dropped.
trace_state implements a similar strategy in regard to tracing events per singe
session.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
